Browsing by Author "Barbosa, Castro"
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- Fibropapillomatosis and the Chelonid Alphaherpesvirus 5 in Green Turtles from West AfricaPublication . Monteiro, Jessica; Duarte, Margarida; Amadou, Kidé; Barbosa, Castro; El Bar, Nahi; Madeira, Fernando Miguel; Regalla, Aissa; Duarte, Ana; Tavares, Luís; Patrício, Ana RitaFibropapillomatosis (FP) is a tumorigenic panzootic disease of sea turtles, most common in green turtles (Chelonia mydas). FP is linked to the chelonid alphaherpesvirus 5 (ChAHV5) and to degraded habitats and, though benign, large tumours can hinder vital functions, causing death. We analyse 108 green turtles, captured in 2018 and 2019, at key foraging grounds in Guinea-Bissau and Mauritania, West Africa, for the presence of FP, and use real-time PCR to detect ChAHV5 DNA, in 76 individuals. The prevalence of FP was moderate; 33% in Guinea-Bissau (n = 36) and 28% in Mauritania (n = 72), and most turtles were mildly affected, possibly due to low human impact at study locations. Juveniles had higher FP prevalence (35%, n = 82) compared to subadults (5%, n = 21), probably because individuals acquire resistance over time. ChAHV5 DNA was detected in 83% (n = 24) of the tumour biopsies, consistent with its role as aetiological agent of FP and in 26% (n = 27) of the ‘normal’ skin (not showing lesions) from FP turtles. Notably, 45% of the asymptomatic turtles were positive for ChAHV5, supporting multifactorial disease expression. We report the first baselines of FP and ChAHV5 prevalence for West Africa green turtles, essential to assess evolution of disease and future impacts of anthropogenic activities.
- Fine-scale foraging segregation in a green turtle (Chelonia mydas) feeding ground in the Bijagós archipelago, Guinea BissauPublication . Madeira, Fernando Miguel; Sampaio e rebelo, Rui; Catry, Paulo; Neiva, João; Barbosa, Castro; Regalla, Aissa; Patrício, Ana RitaGreen turtles (Chelonia mydas) are highly dependent on neritic foraging areas throughout much of their life. Still, knowledge of recruitment dynamics, foraging habits, and habitat use in these areas is limited. Here, we evaluated how the distribution and food preferences of green sea turtles from different life stages varied within a foraging aggregation. We focused on two islands in Guinea-Bissau, Unhocomo and Unhocomozinho, using water captures and survey dives to record habitat use and characteristics, and stable isotopes to infer diet. Additionally, we used stable isotopes to infer their diet. Two habitat types were sampled: deeper (2.26 ± 0.4 m) rocky sites fringed by mangrove with macroalgae, and sandy shallows (1.37 ± 0.12 m) surrounded by rocky reefs with macroalgae and seagrass. The two benthic communities were similar isotopically and in terms of species composition, except for the presence or absence of seagrass, which had unique signatures. We captured 89 turtles ranging from 35 cm to 97 cm in curved carapace length (i.e., juvenile to adult stages). Size distribution was habitat-dependent, with most smaller turtles present in sandy shallows and larger turtles favoring slightly deeper rocky sites. Turtle isotopic signatures differed between the habitat of capture, regardless of size, revealing a marked dichotomy in foraging preference. All turtles fed primarily on macroalgae, mostly rhodophytes. However, individuals captured in sandy habitats had evident seagrass skewed isotopic signatures. Larger turtles may be unable to use the more diverse shallower foraging sites due to increased vulnerability to predation. Despite the proximity of the sampled foraging sites (2.7 km apart), the two foraging subgroups seem to maintain consistently different feeding habits. Our study highlights how heterogeneous green turtle foraging habits can be within populations, even at small geographic scales.
- How to Reduce the Risk of Predation of Green Turtle Nests by Nile MonitorsPublication . Sampaio, Manuel Sá; Sampaio e rebelo, Rui; Regalla, Aissa; Barbosa, Castro; Catry, PauloABSTRACT. – Predation of nests and hatchlings can significantly reduce sea turtle reproductive output. On Cavalos island, João Vieira and Poilão Marine National Park (PNMJVP), Bijagos archipelago, Guinea-Bissau, one of the primary threats to green turtle nests is natural predation, by Nile monitors. In this study, we tested three different nest protection techniques - disguising scent cues, disguising visual cues, and placing a metal net over the nest - to reduce predation on green turtle nests by Nile monitors. Nests were monitored for 10 days after they were laid, and we found that using metal nets and disguising scent cues led to a significant increase of the number of days it took for Nile monitors to find and predate the nests. Overall reduction in predation rates also approached significance when metal nets or disguising scent cues were used. We used the Risk Reduction metric to compare the effectiveness of our experiment with other nest protection techniques; our results corresponded to a >50% decrease of the risk of predation, a value comparable or better than other techniques used elsewhere. We suggest that camouflaging a nest’s scent may be the most cost30 efficient management option to reduce predation rates by Nile monitors in sensitive areas without damaging the local ecosystem.
- Inter-island nesting dynamics and clutch survival of green turtles Chelonia mydas within a marine protected area in the Bijagós Archipelago, West AfricaPublication . Raposo, Cheila; Sampaio e rebelo, Rui; Catry, Paulo; Ferreira-Airaud, Maria Betânia; Barbosa, Castro; Garcia, Tumbulo Bamba; Regalla, Aissa; Sampaio, Manuel Sá; Patrício, Ana RitaUnderstanding spatial heterogeneity in reproductive success among at-risk populations facing localised threats is key for conservation. Sea turtle populations often concentrate at one nesting site, diverting conservation efforts from adjacent smaller rookeries. Poilão Island, Bijagós Archipelago, Guinea-Bissau, is a notable rookery for green turtles Chelonia mydas within the João Vieira-Poilão Marine National Park, surrounded by three islands (Cavalos, Meio and João Vieira), with lower nesting activity. Poilão’s nesting suitability may decrease due to turtle population growth and sea level rise, exacerbating already high nest density. As the potential usage of secondary sites may arise, we assessed green turtle clutch survival and related threats in Poilão and its neighbouring islands. High nest density on Poilão leads to high clutch destruction by later turtles, resulting in surplus eggs on the beach surface and consequently low clutch predation (4.0%, n = 69, 2000). Here, the overall mean hatching success estimated was 67.9 ± 36.7% (n = 631, 2015–2022), contrasting with a significantly lower value on Meio in 2019 (11.9 ± 23.6%, n = 21), where clutch predation was high (83.7%, n = 98). Moderate to high clutch predation was also observed on Cavalos (36.0%, n = 64) and João Vieira (76.0%, n = 175). Cavalos and Meio likely face higher clutch flooding compared to Poilão. These findings, alongside observations of turtle exchanges between islands, may suggest a source-sink dynamic, where low reproductive output sink habitats (neighbouring islands) are utilized by migrants from Poilão (source), which currently offers the best conditions for clutch survival.
- Using fuorescent paint as an effective short-term marker in a high-density rookery of Green Turtles, Chelonia mydas (Linnaeus, 1758), on Poilão Island, Guinea-BissauPublication . Madeira, Fernando Miguel; Sampaio e rebelo, Rui; Barbosa, Castro; Regalla, Aissa; Patrício, Ana RitaWe report on a short-term marking protocol that uses weather-resistant high-contrast fuorescent dyes and nondisruptive ultraviolet lights to effectively mark and distinguish between individual green turtles (Chelonia mydas). We feldtested our method in the largest green turtle nesting location in Africa, on Poilão Island i Guinea-Bissau, where it proved to be quick to apply and easy to detect, and non-disruptive for the turtles. We effectively marked 2719 individuals, with some marks lasting up to 13 days. We propose that this protocol can be adapted for other animal groups and in other environmental settings.